Measurements of gas and aerosol for two weeks in northern China during the winter–spring period of 2000, 2001 and 2002

Intensive measurements of gas and aerosol for 2 weeks were carried out at Qingdao (gas and aerosol in 2000, 2001 and 2002), Fenghuangshan (gas and aerosol in 2000 and 2001), and Dalian (aerosol in 2002) in the winter–spring period. High SO 2 episodes were observed on 18 January 2000 at both Qingdao and Fenghuangshan. According to back trajectory calculations and analysis of gaseous species, high SO 2 episodes were caused by local pollution and transport. Nitrate, sulfate and ammonium were the major species in PM 2.5. Mass fractions of NO 3 −, nss-SO 4 2− and NH 4 + at Qingdao in 2002 were 10%, 12% and 5.5% for PM 2.5, respectively, which were higher than that of nss-Ca 2+ (1%). Chemical compositions observed at Dalian and Fenghuangshan were similar to those at Qingdao. The mass ratio of nss-SO 4 2−/SO 2 at Qingdao in winter was low (< 1.2), indicating that sulfate was probably produced by the slow oxidation of SO 2 in the gas phase and/or was transported from outside of Qingdao in winter. The equivalent ratio of NH 4 + to nss-SO 4 2− was 1.39, suggesting that ammonium sulfate was one of the major chemical compositions in PM 2.5. The NO 3 −/SO 4 2− ratio at Qingdao was higher than that at remote places in East Asia. Gas and aerosol data obtained at Fenghuangshan were similar to data at Qingdao, suggesting that emissions from small cities may have a great influence on pollution in northern China.